Catalyst supports are well known in the art. For example, various clays with high proportions of surface area to volume are known. Representative examples include montmorillonite clays, bentonite clays, Fuller's earth, kaolin clays, sepiolite clays, attapulgite clays, zeolites and mixtures thereof. Silica (sand) is also a commonly used catalyst support. Diatomaceous earth (diatomite; kieselguhr; infusorial earth) is also a common catalyst support. Ceramic-type materials, such as activated alumina, are also known as catalyst supports.
However, a common problem among conventional catalysts, whether used in fixed, fluidized or spouted beds, is that the heat distribution throughout the bed is poor, resulting in "hot spots" in the bed, which at a minimum degrade the product through unwanted side reactions and at worst cause runaway reactions with disastrous results.
Metals are known to provide better heat distribution through bodies of material, but metals are not used as catalyst support because they are also known to have catalytic activity themselves which can catalyze the reactants or products in undesirable side reactions. It is known to use metals themselves as catalysts without separate supports.
U.S. Pat. No. 1,636,685 teaches catalyst carriers having paticles of metallic iron coated with an iron aluminum alloy. Catalyst carriers of aluminum are mentioned as having been proposed but rejected in the prior endeavors.
The efficiency of fixed-bed catalytic chemical reactors usually depends on a variety of parameters, such as temperature, pressure, flow rate and the like, as well as the composition of the mixture of reactants which are fed to the reactor. In some instances, during the design and experimentation of the process, the efficiency of the reaction may still be improving when the practical limit of one or more of the parameters is reached. For example, during development it might be determined that it would have been desirable to make the reaction chambers larger in cross-section to increase the volumetric flow rate of gases through them. However, it may be discovered that larger chambers and flow rates result in disruption of the catalyst column in such a way that effective contact between the catalyst particles and the resulting gas mixture is lost. Movement of catalyst particles in response to the increased force of the gases pushing up on them may be sufficient to cause the catalyst column to "crack" vertically, forming a vertical channel in the direction of flow through which the gases are preferentially directed. Under these conditions, an abrupt drop in the efficiency of conversion of the reactants to product may occur, and the resulting yield of product may become low and unsatisfactory. Furthermore, once the channel has formed, the catalyst column cannot repair itself and can only be restored to its original efficiency by repacking.
A number of fixed bed structures are known. U.S. Pat. No. 3,595,626 notes that ceramic honeycomb placed within or on top of a packed bed, particularly a catalytic bed, improves the effectiveness of the bed. Such honeycomb structures may be fabricated by corrugating sheets of aluminum foil coated with fluxing agent and placing the corrugated sheets together node to node. Ceramic honeycombs dispersed throughout the bed were found to prevent plugging and/or channeling. The catalyst was loosely packed in the bed.
Checkerwork sections within a catalyst bed are used to heat the contents of the bed by induction according to U.S. Pat. No. 2,443,423. U.S. Pat. No. 1,686,349 teaches a process for conducting gaseous catalytic reactions and apparatus therefore which employs perforated partitions of heat insulating material transverse to the direction of flow. In both of these patents, the catalyst bed resided between the sections or partitions in loosely arranged form.
U.S. Pat. No. 1,030,508 describes a contact chamber with a catalyst bed portion having a plurality of perforated plates held at a distance apart from each other by distance pieces. The catalytic material was loosely packed on each plate.
A gas generator which comprises a heat resistant housing and a reaction chamber which is centrally arranged therein and contains a catalytic charge, with an inlet opening for the reactants and an outlet opening for the fuel gas is used for catalytically reacting liquid, hydrocarbon containing fuel to be evaporated with an oxygen containing gas at elevated temperature to form a fuel gas is described in U.S. Pat. No. 4,236,899. The housing of this generator consists of a lower part and a removable cover and the reaction chamber including the catalytic charge is replaceable. The fuel and/or the oxygen containing gas is fed to the reaction chamber for preheating and evaporating, respectively, via a system of tubes which is arranged between the reaction chamber and the lower part of the housing and is run around the reaction chamber in a helical fashion. The reaction chamber contains a packed bed with a plurality of plates having passage canals, the catalytic charge resting upon the plates.
It is known to oxidize propylene to acrolein using catalysts containing copper, bismuth, antimony, tin, molybdenum and mixtures thereof, particularly the oxides of these metals. Dilute solutions of acrolein are produced on site and on demand by oxidizing propylene in an improved reactor using an improved catalyst, which is a mixture of molybdenum, bismuth and tellurium oxides according to U.S. Pat. No. 5,081,314 to Charles L. Kissel and Charles M. Finley of CNC Development, Inc. The catalyst is deposited on metal particles, which are of a metal selected from the group consisting of aluminum, tantalum, titanium, tungsten, niobium and mixtures thereof, and are packed to form a catalyst bed which provides improved heat transfer and distribution for better control of the process. The reaction is conducted in a reactor in which all the exposed surfaces are made of a metal selected from the group just mentioned. The produced acrolein is absorbed to form a dilute solution of acrolein in a liquid to be treated, such as irrigation water for weed control, or control of hydrogen sulfide in water used for oil and gas field water floods, or in fuel oil to inhibit growth of organisms.
It would be desirable if further improvements could be made in the structure of fixed bed catalytic chemical reactors to prevent channeling in a simple manner.